1. Field of the Invention
The invention relates to an inkjet ink, and, for example, relates to a polyamic acid composition for forming an insulating film layer in the production of an electronic component, to a polyimide film formed using the composition, to a film substrate on which the polyimide film is formed, and to an electronic component including the film substrate.
2. Related Art
Polyimide is a material that is widely used in the field of electronic communications because of its excellent heat resistance and electrical insulating properties (see, for example, Japanese Laid-Open Patent Applications 2000-039714, 2003-238683, and 2004-094118). When polyimide is used as a film in the desired pattern, the common approach in the past has been to form the pattern by etching or using a photosensitive polyimide, but this requires large amounts of various chemicals, such as a photoresist, developer, etching solution, and release solution, and furthermore it required a complicated process. Consequently, methods have been studied in recent years for forming a film in the desired pattern by inkjet process.
Various kinds of ink have been proposed for inkjet use (such as in Japanese Laid-Open Patent Applications 2003-213165 and 2006-131730), but if an attempt is made to prepare a polyimide-based inkjet ink, the solvent included in the ink is limited to being N-methyl-2-pyrrolidone or another such amide-based solvent, which leads to decreased durability of the inkjet head and to lower jetting accuracy.
Also, since a polyamic acid has relatively large molecules, preparing an ink with the optimum viscosity for use as an inkjet ink requires the proportion of solvent to be increased so as to reduce the polyamic acid content in the ink. This process was a problem in that it reduced the thickness of the film obtained in a single ink jetting.